1. Field of the Invention
The present invention relates to communication network apparatus such as is used to link together information handling systems or computers of various types and capabilities and to components and methods for data processing in such an apparatus. The present invention includes an improved system and method for scheduling the distribution of information units from a flow control system coupled to a plurality of network processing unit toward a data transmission network through a MAC. More particularly, the present invention involves scheduling using a plurality of algorithms to handle a plurality of users who are processing variable size information packets or frames, providing an order to the frames being provided from the flow control system (which may be of the type described in the referenced Flow Control Patent) toward the data transmission network while allowing for a plurality of different priorities to be accorded to the different users.
2. Background Art
The description of the present invention which follows is based on a presupposition that the reader has a basic knowledge of network data communications and the routers and switches which are useful in such network communications. In particular, this description presupposes familiarity with the International Standards Organization (xe2x80x9cISOxe2x80x9d) model of network architecture which divides network operation into layers. A typical architecture based on the ISO model extends from a Layer 1 (which is sometimes referred to a xe2x80x9cL1xe2x80x9d) being the physical pathway or media through which signals are passed upward through Layers 2 (or xe2x80x9cL2xe2x80x9d), 3 (or xe2x80x9cL3xe2x80x9d), and so forth to Layer 7 which is the layer of application programming resident in a computer system linked to the network. Throughout this document, references to such layers as L1, L2, L3 are intended to refer to the corresponding layer of the network architecture. The present description also is based on a fundamental understanding of bit strings used in network communication known as packets and frames.
Bandwidth considerations (or the amount of data which a system can handle in a unit of time) are becoming important in today""s view of network operations. Traffic over networks is increasing, both in sheer volume and in the diversity of the traffic. At one time, some networks were used primarily for a certain type of communications traffic, such as voice on a telephone network and digital data over a data transmission network. Of course, in addition to the voice signals, a telephone network would also carry a limited amount of xe2x80x9cdataxe2x80x9d (such as the calling number and the called number, for routing and billing purposes), but the primary use for some networks had, at one point in time, been substantially homogenous packets.
A substantial increase in traffic has occurred as a result of the increasing popularity of the Internet (a public network of loosely linked computers sometimes referred to as the worldwide web or xe2x80x9cwww.xe2x80x9d) and internal analogs of it (sometimes referred to as intranets) found in private data transmission networks. The Internet and intranets involve transmission of large amounts of information between remote locations to satisfy an ever-growing need for remote access to information and emerging applications. The Internet has opened up to a large number of users in geographically dispersed areas an exploding amount of remote information and enabled a variety of new applications, such as e-commerce, which has resulted in a greatly-increased load on networks. Other applications, such as e-mail, file transfer and database access further add load to networks, some of which are already under strain due to high levels of network traffic.
Voice and data traffic are also converging onto networks at the present time. Data is currently transmitted over the Internet (through the Internet Protocol or IP) at no charge, and voice traffic typically follows the path of lowest cost. Technologies such as voice over WP (VoIP) and voice over asynchronous transfer mode or ATM (VoATM) or voice over frame relay (VoFR) are cost-effective alternatives for transmission of voice traffic in today""s environment. As these services migrate, the industry will be addressing issues such as the changing cost structure and concerns over the trade off between cost of service and quality of service in the transmission of information between processors.
Aspects of quality of service include the capacity or bandwidth (how much information can be accommodated in a period of time), the response time (how long does it take to process a frame) and how flexible is the processing (does it respond to different protocols and frame configurations, such as different encapsulation or frame header methods). Those using a resource will consider the quality of service as well as the cost of service, with the tradeoffs depending on the situation presented. It is desirable to allow a variety of different priorities or scheduling algorithms to a user, with the user deciding whether he wants (and will pay the changes associated with) a guaranteed bandwidth, best effort, or a guaranteed bandwidth with best effort for peak. In addition, it is desirable that a system for allocating bandwidth have a system for enforcing the priorities and bandwidth which have been selected by a user by denying the user capacity in excess of that which the user has selected and paid for.
Some prior art systems handle outgoing information units from a processing system in a variety of ways. One suggestion is to use a round robin scheduler with fairness amongst a set of queues. Another one employs several different levels of priorities and a queue for each. In such a system, you have an absolute priority where the highest priority work is processed first and the lowest priority work may never get serviced. Still another method of scheduling outputs involves a plurality of prioritized lists. It is also known to use a hierarchical packet scheduling system. There are even systems which use several different scheduling methods in determining the order in which information units are to be sent toward a data transmission network, using a combination of different scheduling techniques.
Other systems have used a weighted priority technique implemented in the form of a round robinxe2x80x94which serves all queues, with some queues served more frequently than other queues, based on an algorithm which defines the level of service. Even such a weighted priority system would provide service to a user who continually exceeds the service levels assigned to it, continuing to serve, albeit less often, even as it exceeds the assigned service level and making it difficult for the system to enforce a level of service policy.
Considering the size of a packet or frame in determining which customers to serve adds a measure of fairness to a service system, in that a user who is processing large frames takes up more of the system capacity and therefore should receive service less often than a user with small frames. Some of the prior art systems consider the size of the transmission in allocating resources, while others do not. Some communication systems use a uniform, fixed-size packet, making consideration of packet size unnecessary, but others do not consider the size of the packet in allocating resources.
Other prior art system are directed to handling information units which are of a common size as in the so-called Asynchronous Transfer Mode (or ATM) system, so that size of the information unit is not considered in determining the priority of the current or a future information unit. An ATM system with a weight-driven scheduler is one of the solutions which is known in the prior art to schedule outputs from an ATM system.
In any such system, it would be desirable to accommodate system constraints like allocating a certain guaranteed bandwidth to a customer, regardless of frame size, while providing a mechanism to provide the following additional features: accommodating peak inputs which exceed the guaranteed bandwidth while providing protection for large and persistent exceeding of a system parameter and yet efficiently and equitably use the capacity of the network processor to provide outputs to the data transmission network.
It would be desirable to have a system which has maximum flexibility to allow for different types and levels of service as desired. For example, some users want a minimum bandwidth, others might want a minimum bandwidth but allows for bursts, still others may be interested in an economy service which provides for a xe2x80x9cbest effortxe2x80x9d service, either with or without a minimum bandwidth, and any limits on bandwidth or burst size must be enforceable by the scheduling system. It would be desirable if a scheduling system could have any or all of these features in a simple and efficient system which accommodates variable packet length and provides for a weighted fair queueing system of allocating unused bandwidth, but, unfortunately such systems do not exist in the prior art.
Thus, the prior art systems for handling data packets for transmission to a network have undesirable disadvantages and limitations which had an effect either on the versatility of the system or the speed with which it could operate.
The present invention overcomes the disadvantages and limitations of the prior art systems by providing a simple, yet effective, way of handling information units or frames coming out of a processing system and directing frames to output ports for dispatch to a data transmission network. The present invention has particular application to a system in which packets of variable length are being handled from a plurality of users and where a level of service commitment has been made to at least some of the users.
The present invention allows the use of multiple types of service level agreements or commitments made to different users of the system. That is, a minimum guaranteed bandwidth could be provided to one user while other users enjoy shared bandwidth, a peak bandwidth could be permitted for a limited duration of time and maximum burst level service could be provided to a user, all as programmed and without interfering with the service provided to other users.
The present invention has the advantage that it allows the efficient use of bandwidth resource and allows service level commitments to be fulfilled while allowing any remaining bandwidth to be used efficiently and equitably.
The present invention also has the advantage of enforcing resource allocations while accommodating bursts. That is, a user can transmit some amount of traffic at a burst rate which exceeds his defined bandwidth for a limited period of time, but, if the user does so for a prolonged period, that user is prohibited from transmitting in excess of his normal bandwidth until he has compensated for the excessive usage. This is accomplished through a system of xe2x80x9ccreditsxe2x80x9d for the flow queue for the respective user which have built up while the user was not using his full bandwidth.
The present system also has the advantage of providing a push down stack in which the latest request for service scheduled for a given time slot or cycle is given priority. This is based on the assumption that the user scheduled later must have a higher priority and any delay in serving that user would be a greater percentage delay than a similar delay in serving a lower priority user. Use of this last-in-first-out (LIFO) system for fulfilling slot requests allows the system to minimize the perceived delay in service as a percentage of the normal intervals between successive service when the system overloaded, that is, it has more work than can be handled at the scheduled time.